1. Field of the Invention
The invention relates to an electron-optical device comprising a cathode ray tube having a target for electrons (for example, a luminescent phosphor screen arranged at the inner side of a transparent window) with an electron gun arranged opposite the target for producing an electron beam, a focusing lens for focusing the electron beam on the target and means for causing the electron beam to scan the target.
2. Description of the Related Art
For a number of applications, particularly those in picture display devices, the cathode-ray tube still has a number of unique advantages such as a high light output, easy addressability and a wide dynamic luminance range. For display devices displaying a large and fiat picture, projection systems using three (monochrome) projection tubes have come into use.
For future applications it would be desirable to have (projection) tubes which can produce sharp images with more light output. There are special electron guns with which small spots can be made, using a large beam current. The envisaged object could be realised if it were not for the fact that the phosphor cannot stand this high load (larger beam current and higher current density) and will be saturated so that the light output does not increase proportionally with the beam current.
A solution would be to increase the scanning frequency (from 16 kHz to, for example, 32 or 64 kHz). However, this presents other problems because the energy required to deflect the beam reaches such high values at high frequencies that this beam is no longer suitable for the deflection (coil) system.